1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling a cell selection and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmission/reception, UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In certain situations, the UE needs to perform a cell selection to select a cell before performing communications via the cell. The situations may be that the UE is just turned on, the UE is not used for a long time, or the UE is new without any registration history. However, the requirement for completing the cell selection is strict, e.g., the cell selection needs to be completed within hundreds of milliseconds (e.g., 600 ms). The UE may not meet the requirement when the UE is not in a good environment or when capability of the UE is not good enough, e.g., the UE is a low cost device (e.g., machine type communication (MTC) device). Accordingly, the UE may need to perform the cell selection for a great number of times. As a result, the UE may need to spend a long time completing the cell selection, resources (e.g., power) for performing the cell (re)selection may be wasted, and the UE may not able to find a suitable cell for camping.
Thus, the cell selection with corresponding requirement (i.e., legacy mode or normal mode) defined in the 3GPP standard may not be flexible and suitable for diverse environments and communication devices.
Thus, how to perform the cell selection efficiently and flexibly is an important problem to be solved.